Update Workbox to 4.1.0

[jadbox]

Currently the generated service worker workbox version is:
importScripts("https://storage.googleapis.com/workbox-cdn/releases/3.6.3/workbox-sw.js")

The latest is 4.1: see https://github.com/GoogleChrome/workbox/releases
The import can now read as:
importScripts("https://storage.googleapis.com/workbox-cdn/releases/4.1.0/workbox-sw.js")

This update improves a number of things, including adding the much needed skipWaiting() message handler:
GoogleChrome/workbox#1929

[r0ughnex]

There are a number of issues with the service worker from the older version of the plugin. I ejected create-react-app and updated the version number in the package.json to 4.1.1 (latest version of workbox-webpack-plugin).

Most of these issues have now been resolved in the new version, and nothing else is required apart from updating the version number of the npm module. This should be a relatively simple update.

[iansu]

@r0ughnex would you like to submit a PR?

[r0ughnex]

@iansu: Sure, I'll take this one up.

[r0ughnex]

@iansu: One more thing, I was having this issue on Chrome (on Windows 10) with version 3.6.3, but updating it to 4.1.1 resolved it. I can't reference the issue. It was auto-lock closed because it went stale.

[r0ughnex]

@jadbox, @iansu: PR submitted for this issue.